Cable Thermal Withstand

Refer to your local regulation!

What is cupper cable? There are English spell-checkers. Did you know that?

eg. what is the maximum current that a 4mm2 cupper cable can hold for a certain time (thermal energy that can pass) ,from where can i get these data ??

http://www.powerstream.com/Wire_Size.htm

Lazy, lazy, lazy!

From your local electrical standards, regulations and cable manufacturer websites.

All of the requirements and de-rating factors (specific to your local electrical codes and application) are available there.

Excellent. I had seen that publication before, but forgot the title and publisher. Thanks for bringing it back to mind.

All of the foregoing are absolutely correct. I add one more. Sizing a wire too tight, because code allows it is more often than not, idiotic.

The most pernicious example is a 480V 200A feeder to my floor. It was undersized, more exactly, it was used with less power before, that somebody - in his infinite wisdom - put the higher load on it. The cable was quite warm - within specs - and I saw it on infra. The trouble developed on my floor's feeder's main breaker. Oxidization at the screw-on contacts of the breaker was not controllable. The workaround and replacement did cost many $100thousands and a year and half work of a couple of people, including me.

Cost effective? NAH, not on your life!!

The formula is K2S2 = I2t

where,

S = Conductor Cross-section, in sq.mm

I = Fault Current, in Amperes

t = Fault Duration, in seconds

K = Adiabatic Constant

= 115 for PVC/Copper

= 143 for XLPE/Copper

= 76 for PVC/ ALuminium

= 92 for XLPE/Aluminium